Starch plant

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Part of an amylopectin polymer
Section from an amylose polymer
Potato field

As starch crops are crops referred to organs with a high content of starch have. Economically important are z. B. the tubers of potatoes , the grains of cereals (wheat, maize) and the fruits or storage tissues of many other species. Starch is often an important part of human and animal nutrition. It is also a renewable raw material (Nawaro) that can be used both materially and energetically ( starch as a renewable raw material ). Part of the starch is obtained in purified form and used primarily in the food industry and for material use. Starch is a polysaccharide (multiple sugar) from the monosaccharide (simple sugar) glucose (grape sugar). Depending on the type, starch consists of branched amylopectin and linear (unbranched) amylose in different proportions .

Starch-producing plants

Wheat and barley stand
Corn field

Different types of plants store the starch in different parts of the plant. Important starch plants are listed below sorted by storage organ.

Turnips, tubers, roots, rhizomes

Above-ground shoot axes

Seeds

Seeds in the pulp

Function of starch in the plant

Isolated starch granules at 800x magnification

The glucose polymer starch is used by land plants and green algae to store energy. Unlike glucose, starch is insoluble and therefore osmotically ineffective. This enables more compact storage. The starch occurs in the most diverse tissues of all green plants . In the case of red algae, on the other hand, there is a form of starch (Florideophycean starch) that varies in the degree of branching. Most other organisms use other reserve materials ( diatoms , golden algae and brown algae : chrysolaminarin (glucose polymer); Euglena: paramylon (glucose polymer); Cryptophyceae : oils in the cytoplasm , starch in the periplastid space). Soluble starch is found in the epidermal cells of some higher plants, which can be detected with iodine ( iodine test ). Mostly, however, starch occurs in granular form, especially in tissues for reserve material storage ( seeds , tubers , onions and rhizomes as well as the wood rays and the wood parenchyma in the wood body of the trees ). This reserve starch is larger-grained than starch in assimilating tissues. The starch granules form within the plant cells in chloroplasts or in other plastids , such as e.g. B. the colorless leukoplast . The latter are mainly found in chlorophyll-free storage tissues in which assimilation products are converted into reserve starch (e.g. in potato tubers) and are also known as amyloplasts . With many algae containing chlorophyll , e.g. B. in Spirogyra , the starch grains occur in special centers of formation in the vicinity of pyrenoids . The initially tiny starch grains grow either through the storage of new starch molecules between the existing ones, or (in the case of composite starch grains) through subsequent fusion and rearrangement with new layers.

Gaining strength

Raw material plant Starch content
(in% of the plant parts used)
pea 40
barley 75
potato 82
Corn 71
manioc 77
rice 89
rye 72
Sorghum 74
sweet potato 72
Triticale 74
wheat 74

The world's most important starch crops are potatoes , corn and wheat . In some countries manioc ( tapioca , also cassava), rice and sweet potatoes play a bigger role. These plants represent the bulk of the world's production of isolated starch of around 45 million tons. There are also other types of grain ( barley , rye , triticale ), peas , sago palms ( sago ) and yams , which are primarily used as starch suppliers for food and feed purposes. In Germany, around 1.53 million tonnes (Europe: 9.4 million tonnes) of starch were produced in 2008, with the largest share coming from potatoes (42%), followed by wheat (33%) and corn (25% ) (Europe: 16% / 37% / 47%). The processed amount in Germany was 1.82 million t (Europe: 8.8 million t), of which 56% was used for food production, 34% in paper production and 10% for chemical, fermentation and technical industries (Europe: 60% / 25% / 15%).

The proportions of amylopectin and amylose in starch vary depending on the type and variety of starch plant. Since amylopectin is primarily required for industrial use, starch plants with the highest possible amylopectin content are preferred. Some types of barley, the starch of which is 95% amylopectin, are based on conventional breeding methods. In the EU, the genetically modified starch potato variety Amflora , whose starch consists almost exclusively of amylopectins, has been in the approval process since 1996 .

The starch is obtained by washing out the starch granules. These grains also contain other constituents of the plastids in which they were formed so that there is no high purity starch. The different types and varieties differ not only in their starch content, but also in the composition of the starch and the content of other ingredients such as proteins , lipids and minerals, as well as the moisture content of the untreated starch. These ingredients usually make up about one percent, the moisture is between 10 and 20% of the starch mass. The required moisture content and ingredients are set out in national and international standards.

(to use the purified starch see article starch )

swell

  1. ↑ Article Starch and Starch, Composition. In: Hans Zoebelein (Ed.): Dictionary of Renewable Resources. 2nd edition, Wiley-VCH, Weinheim and New York 1996; Pp. 265-266, 267, ISBN 3-527-30114-3 .
  2. ↑ Figures and data on the German starch industry. Information from the Association of Starch Industry eV
  3. ↑ www.bioSicherheit.de: GM starch potatoes as a renewable raw material: Amflora - a potato for industry. Retrieved on 200904-08.

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